Frida Kahlo's painting "Niña Con Collar" (1929) has been missing for 60 years—in fact, the only reason it was known to exist at all is because of a photo of it. The artwork has been rediscovered, however, and now its history has been revealed. Since 1955, "Niña Con Collar" has been with one of Kahlo's former assistants—a gift from Diego Rivera. When the assistant left Mexico with the precious painting, nobody took notice—partly because Kahlo wasn't yet famous, and partly because of the relaxed national patrimony protection laws of the time. Up for auction next week via Sotheby's, the painting is expected to sell for over $1.5 million. Read more at Artsy.